Modern electromagnetic communications, surveillance and sensing increasingly rely on array antennas for interfacing or transducing between guided and unguided or freely propagating electromagnetic waves. The advantages of array antennas include the potential for large aperture with relatively light weight, instantaneous beam scanning, and multiple simultaneous beams, including “mbnopulse” operation.
The beam scanning attribute of array antennas requires that the phases of electromagnetic radiation applied to or from each elemental antenna of the array be controlled or adjusted, and these adjustments are performed by electromagnetic radio-frequency (RF) “phase shifters,” where the definition of the term “RF” now includes all frequencies below light frequencies. The general background of the use of phase shifters and array antennas is described in U.S. Pat. No. 5,093,667, issued Mar. 3, 1992 in the name of Andricos. The use of phase shifters in conjunction with an array antenna for monopulse applications is described in U.S. Pat. No. 5,017,927, issued May 21, 1991 in the name of Agrawal et al.
The number of phase shifters in a phased-array antenna system may be as great as twice the number of antenna elements, in order to provide different phase shifts for transmitted and received signals. The cost of phase shifters may represent a major portion of the cost of an array antenna system. A common and relatively inexpensive type of phase shift bit is an ordinary transmission line, well known in the art, having a time delay equal to the desired phase shift at the frequency of operation. A plurality of such transmission lines can be intercoupled with electronic switches to form a multibit or digital phase shifter. In such an arrangement, several phase shifters are intercoupled, having different phase shifts, such as 180°, 90°, 45°, 22½°, and 11¼° for a 5-bit phase shifter. Such a combination of phase shifts can be combined to produce any desired phase shift ranging from 0° to 360°, with no more than about 60 of phase error. Naturally, more bits can be used if a smaller phase shift maximum error is desired. A disadvantage of such transmission-line phase shifters is that they tend to introduce transmission loss into the signal traversing the phase shifter. Another disadvantage of such transmission-line phase shifters is that the bandwidth of the phase shifter depends on its length. Details of a three-bit switched transmission line phase shifter are described in U.S. Pat. No. 4,754,265, issued Jun. 28, 1988 in the name of Henderson et al.
Other types of electromagnetic phase shifters are known. Phase shifters directly controlled by light are described in U.S. Pat. No. 4,675,628, issued Jun. 23, 1987 in the name of Rosen. Electromagnetic phase shifters in which the signal is phase shifted, amplitude controlled, and combined to produce the phase shifted signal are described in U.S. Pat. No. 4,994,773, issued Feb. 19, 1992 in the name of Chen et al.
Improved or alternative phase shifter configurations are desired.